Pfizer will use CytomX Therapeutics’ Probody drug-development platform under an up-to-$635 million collaboration by the companies to develop and commercialize several antibody-drug conjugates (ADCs) for cancer.

The platform is designed to produce what the biotech calls Probody™-Drug Conjugates (PDCs),  ADCs engineered to combine cytotoxic agents with masked “Probodies”—fully recombinant, masked antibodies that remain inert in healthy tissue but are activated specifically in tumors and other disease microenvironments.

Under their agreement, Pfizer and CytomX will work together on preclinical research, while Pfizer has exclusive rights to pursue development and commercialization of any selected PDCs.

Pfizer will pay CytomX $25 million in combined up-front cash, research reimbursement, and payments tied to undisclosed preclinical milestones, as well as up to $610 million tied to undisclosed regulatory and sales milestones, plus tiered royalties reaching double digits on potential future sales.

“Pfizer’s investment in CytomX’ emerging Probody Platform is an important component of our overall strategic focus to advancing the next generation of ADCs and reflects the disruptive potential of this approach,” Robert T. Abraham, svp and CSO for Pfizer’s Oncology Research Unit, said in a statement.

The collaboration is Pfizer’s latest instance of teaming up with a smaller biotech to pursue early-stage R&D. On April 2, BIND Therapeutics said it entered into a collaboration with Pfizer to develop and commercialize a new class of highly selective targeted and programmable therapeutics called Accurins™ using select molecularly targeted therapies, in a deal that could exceed $210 million.

Last year, Pfizer agreed to use Nodality’s Single Cell Network Profiling (SCNP) technology to develop new compounds for autoimmune diseases, in a multiyear strategic collaboration agreement that included developing new companion diagnostics. Pfizer agreed in return to pay Nodality an up-front payment, R&D funding, and milestone payments, all undisclosed.

CytomX was created in 2008 as a spinoff of University of California, Santa Barbara, and won $30 million in Series B venture financing two years later led by Roche Ventures and Third Rock Ventures. Last year CytomX received another $11 million in an expanded Series B financing round led by Canaan Partners joined by Roche and Third Rock.

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